The present invention relates to a surface acoustic wave resonator, and in particular to the structure of a bandpass filter or a bandrejection filter having a plurality of transducers, each of which is composed of interdigital finger electrodes disposed on a piezoelectric substrate.
As described above, the surface acoustic wave resonator is composed of transducers having simple-shaped thin metal conductors disposed on the piezo-electric substrate. Accordingly, it is advantageously possible to realize an extremely small-sized resonator having stable characteristics.
Such a surface acoustic wave resonator must have low loss and sharp cutoff in frequency response as the principal characteristics. In other words, the attenuation characteristics must be able to change sharply between the passband and the rejection band (stopband). In addition, the power-resisting property has become especially noticeable recently. That is to say, it has become important for the surface acoustic wave resonator to operate as a predetermined filter in response to a large power signal.
Although various surface acoustic wave resonators are heretofore known, the power-resisting property has not been considered satisfactory. In some resonators, an improved electrode material is used to enhance the power-resisting property. Nevertheless, the surface wave acoustic resonators now under development are 0.5 W or less in rated power.